Aluminum sound record



Patented July 6, 1937 PATENT OFFICE ALUMINUM SOUND RECORD Junius D. Edwards, Oakmont, Pa., assignor to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania.

No Drawing.

Application May 31, 1935,

Serial No. 24,367 13 Claims. (01. 274-46) This invention relates to records for the reproduction of sound, and particularly to sound reproducing records of aluminum or aluminum alloy.

Aluminum records have been known and used prior to the present invention. Such records are made by impressing a sound groove, usually laterally sinuous, in an aluminum surface by means of a diamond stylus or its equivalent.

The stylus may be caused by electrical means to vibrate laterally with a frequency corresponding to the sound being recorded while an aluminum disk is revolved at constant speed beneath the stylus. The stylus is moved across the face of the disk at a uniform speed so that it impresses a uniformly spaced spiral groove in the surface of the disk. When recording by this method, care must be exercised in the selection of the metal, inasmuch as it is necessary for the best results that the metal flow uniformly under the stylus, rather than be cut or torn by the stylus. 'Other methods of recording may be em ployed or the record may be a duplicate formed from a master record or die.

Aluminum records so produced have certain advantages, among which is the fact that the original recording can be used directly for sound reproduction without the necessity of preparing an intermediate master record, as is the custom 00 in recording on wax. Sound can be recorded on and reproduced from aluminum records with good fidelity and excellent tonal quality. Also, the aluminum records are strong, and can be made very thin and light in weight.

35 However, there are certain disadvantageous restrictions on the use of these aluminum records. It is necessary to use wood or fiber needles in reproducing sound from these records, because a steel needle tears or cuts the aluminum surface, resulting in a high level of surface noises. This is a disadvantage, because steel needles, considered apart from the material of the record, serve to reproduce sound with greater fidelity because of their elastic characteristics.

45 In addition, repeated playing of the plain aluminum record, even with fibre needles, results in gradual depreciation of the sound track.

Efforts have been made heretofore to overcome these disadvantages by providing the aluminum 50 sound record with a hard and resistant, electrolytically formed oxide coating. It was thought that such a coating on the surface of the aluminum record would be advantageous, because it was known that these electrolytic oxide coat- 55 ings possess a high degree of resistance to abranew groove in some instances, although such cut ting does not usually continue for long because the average reproducing equipment such as is used in homes, does not develop enough power to keep the tum-table moving under these conditions. A microscopic examination suggests that this cutting and scratching is caused by the slight roughness of the surface of the hard and apparently glasslike oxide coating. The sharp point of a steel needle (or even a fiber needle, to some extent) catches in the minute depressions or pits in such a surface, with the disadvantageous results already noted.

My invention has for its object to provide an aluminum record which has none of the disadvantages of the plain aluminum records previously known, nor of the electrolytically oxidized aluminum records previously attempted, and to provide a method of making such a record. Another object of my invention is to provide an aluminum sound record having greater permanence of the sound track with repeated use than sound records previously known. Another object of the invention is to provide an aluminum sound record with which steel needles may be used without substantially shortening the life of the record, and with satisfactory tone quality and low level of surface noise.

The foregoing objects are accomplished according to my present invention by providing an aluminum sound record having a sound track which is provided witha hard and resistant electrolytically produced oxide coating with its surface characteristics so modified by a treatment after oxide coating that it is not gouged or cut by a steel needle as used in sound reproduction, and that the steel needle travels freely in the sound track.

I will now describe a preferred form of my improved aluminum sound record, and a preferred method of producing it, but it is to be understood that this description is given only by way of example, and that the invention is not limited to these preferred embodiments.

An aluminum disk is first provided with a sound track in a known manner, as by impressing (not cutting) a laterally sinuous spiral groove in the surface by means of a diamond stylus. The record is then treated to form a hard, resistant and minutely porous oxide coating on the surfaces of the sound track. Any one of several of the known oxide coating processes may be employed, but a particular treatment with which I have had good results comprises immersing the record in an electrolyte containing about 7 per cent oxalic acid and about 7 per cent sulphuric acid. The aluminum record, clean and free from grease, is made the anode in the cell containing the electrolyte, and a current density of 12 amperes per square foot is maintained for a period of from 15 to 20 minutes, the temperature being maintained the while at about 75 F. The record is then removed, washed and dried. I have found this treatment very satisfactory, as it produces a very hard resistant coating, but other known treatments also produce coatings suitable for my present purposes.

The oxide coated surface, produced as described hereinabove or otherwise, is then treated with a suitable lubricant, such as ricinoleic acid, stearic acid, or mixtures of the two or other fatty acids with lubricating properties. Any one of several lubricating substances may be used, but I have had especially good results with diluted dispersions of colloidal graphite, such as Aquadag, and with the ricinoleic acid previously mentioned. Light grades of paramn oil may also be used. It will be understood that these materials are named only as examples, and that a wide variety of similar substances will give useful results.

The selected lubricant is distributed on the surface of the oxide coatedv aluminum record, and after a suitable interval to pennit adsorption, the surface is wiped. The oxide adsorbs enough of this material and retains it to such an extent, that even after numerous playings, enough of the lubricant is still stored in the pores of the coating to give the result desired. If the record is heated before application of the lubricant and allowed to cool in contact with the lubricant, it appears that a larger amount of the lubricant is retained. When an aqueous dispersion of colloidal graphite is employed the water evaporates and leaves a film of graphite which may be polished with a soft cloth.

I have found that my improved aluminum sound record having a surface prepared by the method described hereinabove plays easily with a steel needle, without gouging or scratching. This result is quite remarkable in view of the structure and characteristics of the oxide coating revealed by microscopic observations as described above, and the known facts concerning the resistance of an oxide coating to scratching under a sharp point. It could not be predicted from these facts and the available information on lubricants, as the effect is obviously not a matter of mere lubrication. Even yet it has not been definitely proved why my treated oxide coating behaves in so desirable a manner on aluminum records, but several theories may be suggested. It appears that when the oxide coated surface is prepared in accordance with my invention, the steel needle used for reproduction, instead of cutting or scratching the surfaces of the sound track, merely lightly abrades the surfaces during the first playings of the record. With repeatedpiayings, traces of oxide in the form of powder,-which have been removed by the needle by abrasion, probably remain in the sound track, and this powder may be held answer by the material ordinarily used as a lubricant so that it serves in some way to polish the sound track and protect it from excessive wear, and'to prevent gouging or scratching of the surface by the needle. Another possibility-perhaps related-is that the lubricant, in efiect softens a minute surface layer of the oxide coating, so that it may be more readily polished by the steel neer dle.

The first playings of the record are the most critical ones, and adequate lubricant should be applied during this period. This may be sufficient for the life of the record, but additional treatments may be given later if found necessary.

In ordinary practice, the oxide coating will be formed electrolytically over the entire surface of the aluminum record. In the foregoing description I have emphasized that such an oxide coating is formed on the surfaces of the sound track, but I have done this only to make it clear that, for the purposes of this invention, relatively little importance attaches to the coating on other parts of the record.

What I claim is:

1. An aluminum record with a sound track impressed in its surface, said track being uniformly covered with a hard, electrolytically formed coating having a lubricant adsorbed therein.

2. An aluminum disk with a sound track impressed in its surface, said track being uniformly coated with hard, electrolytically formed oxide 1 having a lubricant adsorbed therein.

3. An aluminum disk record with a sound track impressed in its surface, said track being uniits pores.

4. An aluminum disk with a sound track impressed in its surface, the sides and bottom of said sound track being uniformly covered with a hard, electrolytically formed oxide coating having a lubricant adsorbed therein.

5. An aluminum disk with a sound track impressed in its surface, said track being uniformly coated with a hard, electrolytically formed oxide having ricinoleic acid adsorbed therein.

. 6. An aluminum disk with a sound track impressed in its surface, said track being uniformly coated with a hard, electrolytically formed oxide having a fatty acid adsorbed therein.

7. An aluminum disk with a sound track impressed in its surface, said track being uniformly coated with a hard, electrolytically formed oxide having a graphite dispersion therein.

8. An aluminum record for sound reproduction having a sound track impressed in its surface, said track being covered substantially uniformly with a hard, porous, resistant coating of electrolytically formed aluminum oxide having a lubricant adsorbed therein, whereby the record is adapted for repeated and satisfactory use with a steel needle.

9. The method of treating an aluminum record disk having a sound track impressed in its surface, comprising electrolytically forming a hard oxide coating on the surfaces of the sound track and impregnating said oxide coating with a substance having lubricating properties.

10. The method of treating an aluminum record disk having a sound track impressed in its surface, comprising electrolytically forming a hard oxide coating on the surfaces of the sound track and impregnating the coating with ricinoleic acid.

11. The method of treating an aluminum record disk having a sound track impressed in its surface comprising electrolytically forming a hard oxide coating on the surfaces of the sound track and treating the coating with a dispersion of colloidal graphite.

10 electrolytically formed aluminum oxide having a fatty acid adsorbed therein, whereby the record is adapted for repeated and satisfactory use with a steel needle.

13. An aluminum record for sound reproduction having a sound track impressed in its surface, said track being covered substantially uniformly with a hard, porous, resistant coating of electrolytically formed aluminum oxide having a graphite dispersion therein, whereby the record is adapted for repeated and satisfactory use with a steel needle.

JUNIUS D. EDWARDS. 

